This invention relates to electrostatographic reproduction machines, and more particularly to a liquid immersion development (LID) reproduction machine capable of producing stabilized liquid toner images having clean backgrounds.
Liquid electrophotographic reproduction machines are well known, and generally each include a development system that utilizes an ink or liquid developer material typically having about 2 percent by weight of fine solid particulate toner material dispersed in a liquid carrier. Liquid electrophotographic reproduction machines as such can produce single color images or multicolor images for transfer onto a recording or copy sheet. The liquid carrier is typically a hydrocarbon. In the electrophotographic process of such a machine, a latent image formed on an image bearing member or photoreceptor is developed with the ink or liquid developer material. The developed image on the photoreceptor typically contains about 12 percent by weight of particulate toner in liquid hydrocarbon carrier. To improve the quality of transfer of the developed image from the photoreceptor to a receiver, the image is first conditioned so as to increase the percent solids of the liquid developer forming the image to about 25 percent. Such conditioning is achieved by removing excess hydrocarbon carrier liquid from the developed liquid image. Such removal, however, must be carried out in a manner that results in minimum degradation of the formed liquid toner image. The conditioned image is then subsequently transferred to a final copy sheet or to a receiver which may be an intermediate transfer member, and then to a recording or copy sheet for fusing thereon to form a hard copy.
Conditioning of liquid toner or LID images as above is necessary in order to remove excess hydrocarbon or carrier liquid from the developed images, and in order to stabilize the images particularly for the subsequent transfer steps. One method and apparatus for removing excess carrier liquid from a LID image as disclosed, for example, in U.S. Pat. No. 3,907,423 involves a biased controlled-velocity roller that is spaced from the developed LID image on the photoconductive surface. With this method and apparatus however, unacceptable amounts of carrier liquid are likely to be left in the LID image, and background areas, if partially developed, will remain uncleaned, and hence appear dirty when the image is transferred to a sheet of paper.
Another method and apparatus for removing excess carrier liquid from a LID image as disclosed, for example, in U.S. Pat. No. 5,028,964 involves a biased squeegee roller that actually contacts the developed LID image on the photoconductive surface. Although this particular method and apparatus can effectively remove desired amounts of carrier liquid from the image, it also unfortunately can tend to result in unacceptable offset of toner from the image to the image conditioning roller if the applied bias is relatively too low, that is, too close to zero or ground. On the other hand, if the bias is too high, that is, far from ground, it can prevent the undesirable offset but it can also result in undesirable background toning, in material breakdown, and in undesired overcharging. It is therefore desirable to have a system that results in effective image conditioning and does not require high biases to prevent offset of toner from the image to the image conditioning roller.